(1. 沈陽工業(yè)大學 材料科學與工程學院，遼寧 110870；
2. 貴州工程應用技術學院，貴州 551700；
3. 中航工業(yè)北京航空材料研究院，航空材料檢測與評價北京市重點實驗室，先進高溫結構材料國防科技重點實驗室，北京 100095)
摘 要: 通過蠕變性能測試和組織形貌觀察，研究了鑄態(tài)TiAl-Nb合金在近750 ℃施加不同應力條件下的蠕變損傷行為。結果表明，合金的組織由不同取向的層片狀γ/α2兩相組成，不同取向層片狀組織的晶界為單一γ相。鑄態(tài)合金在(750 ℃，300 MPa)蠕變期間的變形機制是位錯和孿晶，且位錯在層片狀γ/α2兩相及孿晶中滑移。隨蠕變進行，激活的位錯數(shù)量增加，當蠕變位錯與位錯網相遇，可改變位錯的運動方向，促進發(fā)生位錯攀移，減緩應力集中。在蠕變后期，大量位錯在近相界區(qū)域塞積，引起應力集中，可致使裂紋沿垂直于應力軸的層片狀γ/α2兩相界面萌生與擴展，當不同橫斷面的裂紋通過撕裂棱相互連接，直至發(fā)生斷裂，是合金在近750 ℃蠕變期間的損傷與斷裂機制。
關鍵字: TiAl-Nb合金；組織結構；蠕變；變形機制；損傷特征
（1. Shenyang University of Technology, Shenyang 110870; China;
2. Guizhou University of Engineering Science, Bijie 551700, China;
3. Beijing Key Laboratory of Aeronautical Materials Testing and Evaluation, Science and Technology on Advanced High Temperature Structural Materials Laboratory, AVIC Beijing Institute of Aeronautical Materials, Beijing 100095; China）
Abstract:By means of creep properties measurement and microstructure observation, the creep damage behavior of an as-cast TiAl-Nb alloy during various stresses at temperature near 750 ℃ were investigated. The results show that microstructure of alloy consists of lamellar γ/α2 phases, the boundaries with different orientations located in between the lamellar γ/α2 phases are consisted of γ phase. The deformation mechanism of as-cast alloy during creep at (750 ℃, 300 MPa) is twinning and dislocations slipping, and the dislocations slipping within the twins and lamellar γ/α2 phases. In the latter stage of creep, the quantity of activated dislocations increases, the creep dislocations may react with dislocation networks to change their original moving direction when the ones encounter with the networks, which may promote the climbing of dislocations to delay the stress concentration. In the later period of creep, significant amount of dislocations are piled up in the interfaces of the lamellar γ/α2 phases to cause the stress concentration, which may promote the initiation and propagation of cracks along the lamellar γ/α2 interfaces perpendicular to stress axis to display the feature of the trans-lamellar fracture. Wherein, some cracks on the various cross-secions are connected by tearing edge along the direction of maximum shear stress, up to the creep fracture, which is thought to be the damage and fracture mechanism of alloy during creep at 750 ℃.
Key words: TiAl-Nb alloy; microstructure; creep; deformation mechanism; damage feature
